1. Field of the Invention
The present invention relates to alkylation. In another aspect, the present invention relates to alkylation of isoparaffins utilizing olefins. In even another aspect, the present invention relates to a process for the alkylation of isoparaffins utilizing olefins, which process results in reduced acid consumption. In still another aspect, the present invention relates to a process for the alkylation of isoparaffins utilizing olefins, which process results in an alkylate product having increased octane numbers. In yet another aspect, the present invention relates to alkylation of isoparaffins utilizing olefins by controlling the C.sub.3 to C.sub.5 olefin ratio. In even still another aspect, the present invention relates to alkylation of isoparaffins using C.sub.3 and C.sub.5 olefin separately. In even yet another aspect, the present invention relates to alkylation of isoparaffins utilizing propylene, followed by alkylation of isoparaffins utilizing C.sub.4 and/or C.sub.5 olefins. In still even another aspect, the present invention relates to isoparaffin alkylation utilizing separately, C.sub.3, C.sub.4 and C.sub.5 olefins. In still yet another aspect, the present invention relates to alkylation of isoparaffins with C.sub.3 to C.sub.4 by controlling the C.sub.3 to C.sub.4 olefin ratio.
2. Description of the Related Art
As a result of the curtailment in the use of tetraethyl lead as an octane-improving additive for gasoline, not only has the production of unleaded gasoline increased but the octane number specification of all grades of gasoline have increased as well.
Additionally, recent reformulated gasoline specifications require a reduction in both the Reid Vapor Pressure ("RVP") and the olefin content. Alkylate is a low vapor pressure, high octane gasoline blending component containing essentially no olefins. Thus, alkylate helps refiners meet the new reduced RVP and reduced olefin content specifications. Additionally, alkylate burns cleanly, resulting in lower levels of undesired emissions from gasoline engines.
Isoparaffin-olefin alkylation processes are the key route to the production of these highly branched isoparaffin octane enhancers which are to be blended into gasolines, with alkylate typically comprising 10-15% of the gasoline pool.
Alkylation is a well known refinery process for converting light, gaseous olefins into high-octane gasoline components. Very simply, alkylation involves the addition of an alkyl group to an organic molecule. Thus, an isoparaffin can be reacted with an olefin to provide an isoparaffin of higher molecular weight. Generally, the alkylation of isoparaffins with olefins is accomplished by contacting the reactants with an acid acting catalyst such as hydrogen fluoride or sulfuric acid, settling the mixture to separate the catalyst from hydrocarbons, and further separating the hydrocarbons, usually by fractionation to recover alkylate product. The resulting alkylate product is typically a mixture of C.sub.5 to C.sub.16 isomers, with the exact composition depending upon the isoparaffin and olefin reactants used, as well as process conditions.
As practiced commercially, alkylation most commonly involves reacting an isoparaffin, comprising at least 75 weight percent isobutane and up to 25% isopentane, with C.sub.3 to C.sub.5 olefins in the presence of an acid catalyst, typically either hydrofluoric acid or sulfuric acid. The resulting alkylate product comprises predominately C.sub.7 to C.sub.9 isoparaffins, along with lesser amounts of lighter and heavier isoparaffins in the C.sub.6 to C.sub.16 range, and some isopentane.
Historically, C.sub.4 olefins are preferred for use in alkylation, as they produce the highest octane alkylate with the lowest sulfuric acid catalyst consumption, on the order of about 0.5 pounds per gallon of alkylate product, as compared to propylene or C.sub.5 olefins. In fact, an acid consumption of 0.5 pounds per gallon of alkylate represent about 1/3 of the alkylation operating costs.
Alkylation feeds in which the olefins consist of 100% propylene or 100% amylenes typically result in sulfuric acid catalyst consumption on the order of 1.0 to 2.0 pounds acid/gallon of alkylate produced, representing considerably more than 1/3 of the akylation operating cost. The higher sulfuric acid consumption, and lower octane numbers for the alkylate product, resulting from alkylation with propylenes and amylenes as compared to butylenes, makes these feed stocks economically unattractive, and therefore propylenes and amylenes are generally minimized in the alkyation feed.
However, many refiners have mixed olefins containing large amounts of propylene and/or amylenes which must be alkylated. Additionally, due to reformulated gasoline, Reid Vapor Pressure ("RVP"), D-86 distillation temperatures, and other requirements, increasing amounts of propylenes and amylenes are being alkylated and added to the gasoline pool.
Thus, while C.sub.4 olefins are preferred for use in alkylation because of their low acid consumption, and resulting high-octane alkylate, alkylation with propylene may be necessary to meet product specifications. Other reasons for alkylating with propylene and/or amylenes include their ready availability, and unavailability of sufficient amounts of C.sub.4 olefins for the amount of alkylate desired.
U.S. Pat. No. 2,242,845, issued Aug. 14, 1939 to Blount, discloses a process for alkylation of isobutane with a mixture of propylene and butylenes in the presence of sulfuric acid. For product yield, Blount discloses that the optimum alkylation temperature for alkylation of isobutane with butylene is about 30.degree. F. to about 60.degree. F., and for alkylation of isobutane with propylene is about 70.degree. F. to about 100.degree. F.
U.S. Pat. No. 2,351,464, issued Jun. 13, 1944 to Voorhies Jr. et al., discloses that it is well known to react olefins having from 2 to 5 carbons atoms with saturated hydrocarbons containing a tertiary carbon atom. The '464 patent further discloses that while alkylation with olefins having 3 or more carbon atoms has been entirely satisfactory, alkylation with ethylene has not been satisfactory due to excessive acid consumption. The '464 patent proposes that an acid employed for alkylation of olefins comprising ethylene, be separated and subsequently employed in the alkylation of olefins free of ethylene, without incurring any substantial acid consumption and with acid regeneration.
U.S. Pat. No. 2,491,618, issued Dec. 20, 1949 to Luetzelschwab discloses a catalytic contacting apparatus in which isoparaffinic and olefinic hydrocarbons may be introduced into the apparatus separately or admixed.
U.S. Pat. No. 3,045,055, issued Jul. 17, 1960 to Van Pool et al. generally disclose a process for the alkylation of a isoparaffin and the reforming of a hydrocarbon wherein each operation is arranged to benefit the other. Specifically, the process as disclosed by Van Pool et al. generally includes alkylation of an isoparaffin and an olefin in the presence of a hydrogen fluoride catalyst to obtain an alkylate effluent comprising an alkylate product, organic fluorides and normal isoparaffin. Van Pool et al. disclose that the charge materials introduced into the alkylation zone may include propylene, butylenes, amylenes, isobutane, isopentane, propyl fluorides, butyl fluorides, and amyl fluorides. Van Pool et al. further disclose that the preferred alkylation charge is an olefin-isoparaffin mixture, preferably a butylenes-isobutane mixture.
U.S. Pat. No. 3,211,803, issued Oct. 12, 1965 to Chapman discloses an alkylation process for the elimination of heavy alkylate utilizing both alkylation and reforming, with propylene and/or butylenes disclosed as the preferred olefins.
U.S. Pat. No. 3,502,569, issued Mar. 24, 1970 to Hervert discloses a process for the production of high octane motor fuel by alkylation and reforming. Hervert discloses that alkylation may be carried out by the catalytic alkylation of isobutane and/or isopentane with propylene, butylenes and amylenes. Specifically Hervert discloses alkylating isobutane with C.sub.4 mono-olefin in the presence of an acid catalyst to produce an alkylate product containing dimethylhexanes. This alkylate is then separated into various fractions based on octane content. The lower-octane fraction is then reformed by admixture with hydrogen and a reforming catalyst. Finally, a portion of the reformate is commingled with the high-octane alkylate fraction to produce a suitable motor fuel alkylate. However, Hervert does not disclose or teach the problem of increased acid consumption by propylene, nor disclose or suggest a solution for such increased acid consumption.
U.S. Pat. No. 3,683,041, issued Aug. 8, 1972 to Goldsby, discloses alkylation encountering acidity run-aways. The '041 patent discloses that if run-away acid, the overall acid-hydrocarbon emulsion or reaction mixture produced during a run-away, or the alkylate produced and which contains sulfur, is charged to a normally operating alkylation reaction, that the acid can be restored to alkylation strength by alkylation of the alkyl sulfates, and the hydrocarbon portion of the reaction mixture can be freed of sulfur by extraction and alkylation of the alkyl sulfates.
U.S. Pat. No. 3,778,489, issued Dec. 11, 1973, to Parker et al., discloses an alkylation process which utilizes separate feed streams. Specifically, the '489 patent discloses that olefins which form tertiary carbonium ions under acidic conditions react unfavorably with terminal olefins not able to form tertiary carbonium ions under acidic conditions. According to the '489 patent, high octane alkylate is prepared by contacting a paraffin and a strong alkylation catalyst, in an alkylation zone, with a first olefin-containing stream substantially free of isobutylene and 2-methyl-butene-1 and a second olefin-containing stream comprising isobutylene, 2-methyl-butene-1 or mixtures thereof.
U.S. Pat. No. 3,998,903, issued Dec. 21, 1976 to Sobel, discloses an alkylation process utilizing an olefinic reactant containing 1-butene, 2-butene and isobutylene by fractionating the olefinic reactant into a 2-butene fraction and a separate 1-butene and isobutylene fraction. The 2-butene is charged to an HF alkylation reaction zone with isobutane. The mixture is heated by the heat of reaction, and the fraction comprising 1-butene and isobutylene is then added to the unitary reaction zone.
There is a need in the art for an improved alkylation process.
There is another need in the art for an improved alkylation process in which the acid catalyst consumption can be controlled and/or minimized.
There is even another need in the art for an improved alkylation process in which the octane number of the alkylate product can be controlled and/or maximized.
There is still another need in the art for an improved alkylation process for alkylating propylene or high propylene containing feeds, which is easier to operate than the known processes.
There is yet another need in the art for an alkylation process for alkylating amylene or high amylene containing feeds, which is easier to operate than the known processes.
There is even still another need in the art for an alkylation process for alkylating feeds having mixtures of propylene and amylenes.
There is even yet another need in the art for an alkylation process for alkylating feeds having mixtures of propylene and butylenes.
Other needs of the art will become evident to those of skill in the alkylation art upon reading this specification.